1. Field of Invention
The present invention is concerned with a liquid softening agent for woven fabrics, having excellent stability.
2. Description of Prior Art
Most of the softening agents marketed for household uses are in the form of a liquid composition. The quaternary ammonium salt in the composition possesses two long-chain alkyl groups or .beta.-hydroxyalkyl groups showing an affinity to the water, but a low degree of solubility in water. Therefore, the aqueous solutions having high concentrations of the quaternary ammonium salt are transferred into gels, thus making it hard to obtain a stable composition of a low viscosity. Therefore, a variety of methods have been attempted in order to obtain low viscosity and stable liquid compositions, for example by adding a non-ionic surface active agent, monoalkyl cationic surface active agent, solvent, etc.
For example, Japanese Patent Publication No. 3920/70 discloses a liquid softening agent for woven fabrics composed of a quaternary ammonium salt, a non-ionic surface active agent consisting of an ethylene oxide addition product a higher alcohol, a higher aliphatic acid or alkylphenol, and a solvent such as a lower alcohol, glycerol, glycol, etc. The Japanese Laid-open Patent Application No. 54300/73 proposes to blend an alkyl polyoxyethylenated quaternary ammonium salt or alkyl-betaine to the aforesaid composition to make a softening composition for the purpose of increasing the solution stability and imparting an antistatic property. However, the blend compositions recited in the claims of the above publication and application do not obtain a stable liquid composition, unless there are made present alkali metal salts such as sodium chloride as disclosed in the specification of the present application. Without containing such alkali metal salts, the liquid composition tends to be gelled, making it hard to obtain a desired liquid composition. The blend systems in which there is incorporated alkali metal salts may help obtain a composition having a low viscosity and improved recovery from freezing, but they do not form stable dispersion systems. Therefore, according to such methods, it is necessary to incorporate large amounts of the aforementioned compounds such as non-ionic surface active agent or solvent for the purpose of giving satisfactory dispersion stability and recovery from freezing at any temperatures.
However, the aforesaid stabilizing effect, owing to its hydrotropy effects to the hydrophobic group, develops its effect during the treatment of the woven fabric; therefore, the quaternary ammonium salt is not absorbed sufficiently by the woven fabric, eventually, making it impossible to fully impart the softening effect to the woven fabric.
On the other hand, if the additives are incorporated in small amounts, the resulting composition which may have low viscosity at the time of the incorporation, will cause the dispersed particles to be agglomerated upon heating or freezing and gives rise to the occurrence of creaming or gellation.